Metrology generally involves measuring various physical features of a target component. For example, structural and material characteristics (e.g. material composition, dimensional characteristics of structures and/or critical dimensions of structures, etc.) of the target component can be measured using metrology tools such as scatterometers, ellipsometers, or scanning electron microscopes (SEMs). In the example of semiconductor metrology, various physical features of a fabricated semiconductor component may be measured using a metrology tool.
Once a metrology measurement is obtained, the measurement may be analyzed. This analysis typically involves a library having predefined value(s) for parameters specific to the target component (i.e. a parametric model of the target component). In particular, the library may include value ranges for floating parameters. The library may then be used to provide a fast mathematical approximation that can quickly reproduce the solution of a system having the target component with a reasonable accuracy, given the set of values for the parametric model.
Conventional techniques of calibrating the metrology tools include mechanical calibration of the metrology tool by adjusting various system parameters. For example, the metrology tool may be calibrated by adjusting a focal length of an optical system, adjusting an orientation of polarization, or adjusting other physical system parameters. Some techniques may also require the performance of an optimization procedure to minimize the difference between signals generated by a reference tool and signals generated by a calibrated tool. These optimization procedures are typically limited to adjusting a small number of physical parameters associated with the metrology tool being calibrated until a difference between the signals generated by the metrology tool and a set of reference signals generated by a reference tool are minimized. However, because the optimization procedures typically use a limited number of physical parameters, there may still be significant differences between the signal produced by the calibrated metrology tool and the reference signals. Therefore, there is a need for addressing these and/or other issues associated with the prior art implementations of inspection systems.